Possible reasons for the rise in duodenal ulceration in the nineteenth and twentieth centuries
| Surveillance artefact |
| Environmental cofactors affecting acid secretion and tissue healing (e.g. nutritional changes, smoking, NSAID and aspirin use) |
| Introduction of new Helicobacterstrains |
| Increased acquisition of H pylorifrom non-relatives |
| Change in multiplicity ofHelicobacter colonisation |
| Improved sanitation (impediment to transmission) selected for more virulent strains |
| Diminished H heilmanni cocolonisation |
| Increase in H pylori acquisition age |